Soft tissue paper is generally preferred for disposable paper towels, and facial and toilet tissues. However, known methods and means for enhancing softness of tissue paper generally adversely affect tensile strength. Tissue paper product design is, therefore, generally, an exercise in balancing softness against tensile strength.
Both mechanical and chemical means have been introduced in the pursuit of making soft tissue paper: tissue paper which is perceived by users, through their tactile sense, to be soft. Such tactile perceivable softness may be characterized by, but not limited to, resilience, flexibility, and smoothness; and subjective descriptors such as feeling like silk or flannel. The present invention pertains to a process for improving the tactile perceivable softness of tissue paper--in particular high bulk, creped tissue paper--through the incorporation of chemical additives: in particular, polysiloxane materials which impart a silky or flannel-like feel to the tissue paper without rendering it greasy or oily to the tactile sense of users of products comprising such tissue paper. Additionally, surfactant material may be added to further enhance softness and/or surface smoothness and/or to at least partially offset any reduction in wettability caused by the polysiloxane; and binder material such as starch may be added to at least partially offset reductions in strength and or increasing in linting propensity that results from the polysiloxane and, if used, the surfactant additive.
Representative high bulk, creped tissue papers which are quite soft by contemporary standards, and which are susceptible to softness enhancement through the present invention are disclosed in the following U.S. Pat. Nos.: 3,301,746 which issued Jan. 31, 1967 to Lawrence H. Sanford and James B. Sisson; 3,974,025 which issued Aug. 10, 1976 to Peter G. Ayers; 3,994,771 which issued Nov. 30, 1976 to George Morgan, Jr. and Thomas F. Rich; 4,191,609 which issued Mar. 4, 1980 to Paul D. Trokhan; and 4,637,859 which issued Jan. 20, 1987 to Paul D. Trokhan. Each of these papers is characterized by a pattern of dense areas: areas more dense than their respective remainders, such dense areas resulting from being compacted during papermaking as by the crossover knuckles of imprinting carrier fabrics. Other high bulk, soft tissue papers are disclosed in U.S. Pat. Nos. 4,300,981 which issued Nov. 17, 1981 to Jerry E. Carstens; and 4,440,597 which issued Apr. 3, 1984 to Edward R. Wells and Thomas A. Hensler. Additionally, achieving high bulk tissue paper through the avoidance of overall compaction prior to final drying is disclosed in U.S. Pat. No. 3,821,068 which issued Jun. 28, 1974 to D. L. Shaw; and avoidance of overall compaction in combination with the use of debonders and elastomeric bonders in the papermaking furnish is disclosed in U.S. Pat. No. 3,812,000 which issued May 21, 1974 to J. L. Salvucci, Jr.
Chemical debonders such as those contemplated by Salvucci, referred to above, and their operative theory are disclosed in such representative U.S. Pat. Nos. as 3,755,220 which issued Aug. 28, 1973 to Friemark et al; 3,844,880 which issued Oct. 29, 1974 to Meisel et al; and 4,158,594 which issued Jan. 19, 1979 to Becker et al. Other chemical treatments which have been proposed to improve tissue paper include, for example, that disclosed in German Patent 3,420,940, Kenji Hara et al, to wit: to impregnate toilet tissue paper with a combination of a vegetable, animal, or synthetic hydrocarbon oil, and a silicone oil such as dimethylsilicone oil to make it easier to clean and wipe with.
Additionally, a well known mechanical method of increasing tensile strength of paper made from cellulosic pulp is by mechanically refining the pulp prior to papermaking. In general, greater refining results in greater tensile strength. However, consistent with the foregoing discussion of tissue tensile strength and softness, increased mechanical refining of cellulosic pulp negatively impacts tissue paper softness, all other aspects of the papermaking furnish and process being unchanged. However, through the use of the present invention, tensile strength can be increased without negatively impacting softness; or, alternatively, softness can be improved without negatively impacting tensile strength.
It is an object of this invention to provide a process for preparing tissue paper which has an enhanced tactile sense of softness.
It is another object of this invention to provide a process for preparing tissue paper which has a silky, flannel-like feel.
It is a further object of this invention to provide a process for preparing tissue paper which has increased tactile softness at a particular level of tensile strength relative to tissue paper which has been softened by conventional techniques.
These and other objects are obtained using the present invention, as will be seen from the following disclosure.